The overall goal of this proposal is to continue our efforts in developing and validating reagents and methods suitable for imaging human islets in the context of islet transplantation and/or type 1 diabetes (TID). Functional imaging of the endocrine pancreas has been difficult, in part because of the many physiologic roles and cell types that characterize the Islets of Langerhans and the exocrine pancreas. During the past year (10/2002- 2/2004) we have used transcript profiling to obtain a map of the genes expressed by human islet tissue, human exocrine pancreas tissue, and other tissues. Using novel informatics techniques we have identified previously unrecognized candidate markers on islets previously thought to be restricted to neuronal and neuroendocrine tissues. This data has clearly revealed specific molecular/functional overlaps between islet cells and cells of neural and neuroendrocrine lineage, allowing us to now take advantage of a large body of experience and research that has focused on functional imaging of the CNS. On the basis of our efforts in identifying islet specific markers we now propose that targeting beta cell vesicular monoamine transporters, type 2 (VMAT2) with PET radioligands will provide quantitative measurements of beta cell mass and function. We have three specific aims that together are designed to provide the necessary preclinical data to move islet imaging via VMAT2 targeting into clinical trials as expediently as possible. In specific aim one we outline the necessary steps to establish the radiosynthesis of VMAT2 ligands in our PET chemistry laboratory. Specific aim two focuses on expanding our understanding of the ultrastructural and cell biology of vesicular monoamine transporters type 2 as expressed in beta cells. In specific aim three we outline a series of studies in animal models of diabetes and islet transplantation designed to show proof of principle (i.e VMAT2 targeting provides quantitative measurements of beta cell mass useful for the management and study human type 1 diabetes and islet transplantation). We have drawn together an interdisciplinary research team of basic cell biologists, transplant surgeons and experts in nuclear medicine with the common goal of developing of imaging reagents and techniques that distinguish islets from its surroundings and provide quantitative measurements of their mass.